Chronic exposure of coho salmon to sublethal concentrations of copper--II. Distribution of copper between high- and low-molecular-weight proteins in liver cytosol and the possible role of metallothionein in detoxification.

1. Liver cytosol samples from juvenile coho salmon exposed over a 14-week period to 70 micrograms/l (1/4 LC50) or 140 micrograms/l (1/2 LC50), were separated into high-molecular-weight and low-molecular-weight fractions by column chromatography on Sephadex G-75, and compared to similar samples obtained from control fish. 2. The levels of copper in the low-molecular-weight function of fish exposed to 70 micrograms/l were not significantly increased over control values for the first 6 weeks but then increased rapidly, while those of fish exposed to 140 micrograms/l increased substantially in the first 2-4 weeks of exposure, then levelled off. 3. In the exposed fish the levels of copper in the high-molecular-weight fraction were not significantly elevated above control levels over the first 8-10 weeks but then increased significantly. 4. The low-molecular-weight fractions of exposed fish were shown to contain increasing levels of metallothionein. The metallothionein was isolated on DEAE-cellulose and characterized by amino acid analyses.